Thermal and extraction methods for the treament of the biomass and its separation from the available fatty substances are known. See, Libermann S., V. Petrovskiy, "Spavotshnoe rukovodstvo po proisvodvu technitsheskih fabrikatov na miassokombinatah", Pishtepromizdat, Moskova, str. 92-260 (1961). The thermal methods, which can be devided into "humid" and "dry" methods according to the way of heating the initial biomass are based on the relatively low melting point of the fatty substances, which are separated in molten state from the rest, consisting of the so-called "animal food meal". See, Libermann and Petrovskiy.
The disadvantages of the thermal methods are as follows. There is a low degree of extraction of the fatty substances; from 12 to 18% of unextracted fatty substances remain in the meal, which imposes an additional treatment step. High temperatures are needed to carry out the process, creating conditions for hydrolysis and thermal destruction of the lipids and the other ingredients. There is also a high consumption of energy.
Methods for treatment of the biomass are also known using fish and mussels of low quality, which are directly treated to obtain fish and mussel meals. See, Sakandelidze O., G. Kipiani (redaktori), "Biologitsheski aktivnie veshtestva gidrobintovnoviy istotshnik lekarstv", Shtiintza, kishinev, str. 116-124 (1979); Abadjieva V., sp. "priroda i znanie", kn. 1, str, 12 (1970). Despite their high nutritive qualities, these meals possess an unpleasant specific odor and taste which limits their use as animal food. A special dosage is required because of the worsening of the gustatory qualities of the meat for feeding animals such kinds of meal.
In comparison with the thermal methods, the extraction methods show a more complete separation. See, Libermann and Petrovskiy. The lipids extracted from non-industrial and inferior value marine organisms are treated, and substitutes of fish oils, meals and physiologically active substances are obtained. See, Sakandelidze and Kipiani. These methods are also used to investigate the sterol composition of marine organisms as well as in the extraction of physiologically active substances from them. See, Avt. svidetestvo na NRB, reg. N. 41541/1978.
The disadvantages of the extraction methods are as follows. They use a large amount of organic solvents for the extraction without achieving a complete separation of the lipids (2% remain unextracted). Conditions are created for the formation of stable emulsions and suspensions, which complicate additionally the separation of the lipids form the biomass. The used organic solvents are highly inflammable and harmful to health.
Methods are known using acid (5,6) and enzymatic (5,6) hydrolisis of the protein biomass with the purpose to obtain a semi-synthetical feed for cell culture as well as for obtaining protein hydrolyzate for animal foodstuffs. See, Libermann and Petrovkiy; Avt. svidetestvo na NRB, reg. N. 41541/1978; and Avt. svidetestvo na NRB, reg. N. 46878/1980.
A basic disadvantage of these methods is the fact that the protein hydrolyzates are obtained in the form of total mixtures, containing lipids, nucleic acids and the like. Besides, during the acid hydrolysis the process is further complicated because of the destruction of some of the aminoacids, which involves a lowering of the nutritive value of the obtained hydrolyzates. Chemical modifications also occur with some of the lipid components.
The application of semipermeable membranes for the separation of different kinds of substances from their solution owning to their different molecular weight is also known. See, Hvang S., K. Kamermayer, "Membranie prozesi razdelenia", "Himia", Moskva (1981).